I'm about to throw a spanner into the works.
Funny thing about the whole argument, is that both sides are correct.
Keeper is arguing about 3D images dynamically generated by the PC, where the ratios can be adjusted on the fly without loss of quality.
3D is a vector drawing (or triangles to be precise) with a bitmap texture applied to it and is not dependent on pixel which is why the PC can adjust the FOV without loss of quality.
A 2D example of this is Illustrator or Corel Draw using vector drawings. When you take the pen and draw it, the lines can (zoom in/out or resized) scale without loss of quality. Vectors are stored per point (or within 3D space) and drawn dynamically by the PC (rendering). The PC then translates the information to pixels.
However, for movies (and generally 2D bitmap graphics) information is stored per block (aka pixel). If you open an image in photoshop and zoom in you will clearly see the blocks. Every pixel in the bitmap was precalulated and stored within a certain format and the PC translates the pixel 1:1. Therefor it cannot scale without losing quality. Good example of the was the movie at 1920x1080 vs 1920x1200. (Or Techies' Firefox example).
Here is an example of Vector vs Bitmap:
http://www.sunilpatel.co.uk/images/TeX Help/TeX Vector vs Bitmap.jpg
So for 3D games, you will benefit having more peripheral vision (16:9), since you don't need to see more of the floor and the ceiling. However, the FOV is adjustable. The higher the FOV the wider the camera lens and the more that will be rendered in view. (Example is: Some games use FOV of 65 and some quake players use FOV 105 for more vision (even on 4:3 monitors)) Having a bigger monitor will also allow you to have a bigger FOV. Though, they had to lock the Vertical FOV to accomodate Widescreen monitors so that the image does not go out of aspect. This is the same as when you stretch a 4:3 TV program on your 16:9 TV - everyone looks fat. This is automatically adjusted by the game.
For digital movies the field of view cannot change and as long as your resolution is the same or even larger (provided that you don't scale it up) than the original source, it should display it without loss of quality.